1. Field of the Invention
The present invention relates to a system for measuring a sound velocity in material by means of using a piezoelectric substrate, an interdigital arrangement of two comb-shaped electrodes formed on an upper end surface of the piezoelectric substrate, a counter electrode formed on a lower end surface of the piezoelectric substrate, a frequency-sweep oscillator and a frequency analyzer.
2. Description of the Prior Art
In recent years, ultrasonic techniques for measuring the sound velocity in a liquid are essential in the field of biophysics and medical science as well as physical acoustics, industry, physical chemistry, and others. A thickness mode piezoelectric transducer with parallel plate-like electrodes is commonly used for this purpose. Such a conventional type of transducer needs, for example, a circulator in order to separate a delayed electric signal from an input electric signal, because the conventional type of transducer is used both as input- and output electrodes. Accordingly, such the conventional type of transducer has a difficulty in quick response measurement, and a complicated circuit-construction.
On the other hand, an interdigital transducer on the piezoelectric substrate operates at a liquid-solid boundary as a leaky wave transducer for bulk wave radiation into the liquid. The leaky SAW traveling on a sufficiently thick substrate compared with the wavelength has only one mode without velocity dispersion. Such the interdigital transducer for the leaky SAW has a difficulty in making the radiation angle vertical, so that has a difficulty in measurement accuracy, and stable operation.
An object of the, present invention is to provide a system for measuring a sound velocity in material capable of making an interdigital transducer act as a thickness mode transducer.
Another object of the present invention is to provide a system for measuring a sound velocity in material operating with a quick response.
Another object of the present invention is to provide a system for measuring a sound velocity in material need not a circulator, and so on.
Another object of the present invention is to provide a system for measuring a sound velocity in material capable of making the radiation angle vertical.
Another object of the present invention is to provide a system for measuring a sound velocity in material capable of low electric power consumption.
Another object of the present invention is to provide a system for measuring a sound velocity in material capable of measuring the sound velocity in cellular tissue.
Another object of the present invention is to provide a system for measuring a sound velocity in material excellent in durability and manufacturing.
Another object of the present invention is to provide a system for measuring a sound velocity in material, which is not affected by a change in circumstances, for example, a change in temperature.
A still other object of the present invention is to provide a system for measuring a sound velocity in material easy in use and having a small size which is very light in weight and has a simple structure.
According to one aspect of the present invention there is provided a system for measuring a sound velocity in material comprising a piezoelectric substrate, first- and second comb-shaped electrodes formed on an upper end surface of the piezoelectric substrate, a counter electrode formed on a lower end surface of the piezoelectric substrate, a frequency-sweep oscillator generating input electric signals Ei (i=1, 2, . . . , n) with carrier frequencies fi (i=1, 2, . . . , n), respectively, and a frequency analyzer. The counter electrode is in contact with a surface-part of a material. The first- and second comb-shaped electrodes form an interdigital arrangement.
When the input electric signals Ei are applied between the first comb-shaped electrode and the counter electrode in turn, longitudinal waves are radiated into the material along the direction vertical to the lower end surface of the piezoelectric substrate. If the longitudinal waves are reflected at the opposite surface-part of the material, reflected longitudinal waves are detected between the second comb-shaped electrode and the counter electrode as delayed electric signals Di (i=1, 2, . . . , n), respectively. On the other hand, electrical coupled-signals Ci (i=1, 2, . . . , n) from the input electric signals Ei, respectively, are also detected between the second comb-shaped electrode and the counter electrode. The electrical coupled-signals Ci and the delayed electric signals Di interfere, respectively, so that respective interference signals Ri (i=1, 2, . . . , n) occur. Tracing a dependence of respective amplitudes of the interference signals Ri on the carrier frequencies fi provides a frequency periodicity xcex94f. Thus, a sound velocity V in the material is calculated from the product of the frequency periodicity xcex94f and twice a distance Z between the piezoelectric substrate and the opposite surface-part of the material.
According to another aspect of the present invention there is provided a system for measuring a sound velocity in material further comprising a reflector, which is parallel with the lower end surface of the piezoelectric substrate and in contact with the opposite surface-part of the material.
According to another aspect of the present invention there is provided a system for measuring a sound velocity in material, wherein the ratio of the interdigital periodicity of the interdigital arrangement to the thickness of the piezoelectric substrate is smaller than four times the ratio of the longitudinal wave velocity in the material to the longitudinal wave velocity in the piezoelectric substrate.
According to another aspect of the present invention there is provided a system for measuring a sound velocity in material, wherein increasing the number of electrode-finger pairs in the interdigital arrangement makes the directionality of the longitudinal waves sharper under a condition that the total amount of all the finger-areas of the first comb-shaped electrode is constant.
According to another aspect of the present invention there is provided a system for measuring a sound velocity in material, wherein the material is a liquid matter.
According to another aspect of the present invention there is provided a system for measuring a sound velocity in material, wherein the material is a cellular tissue.
According to another aspect of the present invention there is provided a system for measuring a sound velocity in material further comprising a polymer film, with which the lower end surface of the counter electrode is coated.
According to another aspect of the present invention there is provided a system for measuring a sound velocity in material comprising a first piezoelectric, substrate, a first interdigital arrangement of two comb-shaped. electrodes formed on a lower end surface of the first piezoelectric substrate, a second piezoelectric substrate, a second interdigital arrangement of two comb-shaped electrodes formed on an upper end surface of the second piezoelectric substrate, a counter electrode cemented between the first- and second piezoelectric substrates, a frequency-sweep oscillator generating input electric signals Ei (i=1, 2, . . . , n) with carrier frequencies fi (i=1, 2, . . . , n), respectively, and a frequency analyzer. A lower end surface of the first interdigital arrangement is in contact with a surface-part of a material.
When the input electric signals Ei are applied between one of the two comb-shaped electrodes in the first interdigital arrangement and the counter electrode in turn, longitudinal waves are radiated into the material along the direction vertical to the lower end surface of the first piezoelectric substrate. If the longitudinal waves are reflected at the opposite surface-part of the material, reflected longitudinal waves are detected between one of the two comb-shaped electrodes in the second interdigital arrangement and the counter electrode as delayed electric signals Di (i=1, 2, . . . , n), respectively. On the other hand, electrical coupled-signals Ci (i=1, 2, . . . , n) from the input electric signals Ei, respectively, are also detected between the one of the two comb-shaped electrodes in the second interdigital arrangement and the counter electrode. The electrical coupled-signals Ci and the delayed electric signals Di interfere, respectively, so that respective interference signals Ri (i=1, 2, . . . , n) occur. Tracing a dependence of respective amplitudes of the interference signals Ri on the carrier frequencies fi provides a frequency periodicity xcex94f. Thus, a sound velocity V in the material is estimated from the frequency periodicity xcex94f.
According to another aspect of the present invention there is provided a system for measuring a sound velocity in material, wherein the finger direction of the second interdigital arrangement is orthogonal to that of the first interdigital arrangement.
According to another aspect of the present invention there is provided a system for measuring a sound velocity in material, wherein the finger width in the one of the two comb-shaped electrodes in the first interdigital. arrangement is wider than that in the other of the two comb-shaped electrodes in the first interdigital arrangement, and the finger width in the one of the two comb-shaped electrodes in the second interdigital arrangement is wider than that in the other of the two comb-shaped electrodes in the second interdigital arrangement.
According to another aspect of the present invention there is provided a system for measuring a sound velocity in material further comprising a reflector, which is parallel with the lower end surface of the first piezoelectric substrate and in contact with the opposite surface-part of the material.
According to another aspect of the present invention there is provided a system for measuring a sound velocity in material, wherein the ratio of the interdigital periodicity of the first interdigital arrangement to the thickness of the first piezoelectric substrate is smaller than four times the ratio of the longitudinal wave velocity in the material to the longitudinal wave velocity in the first piezoelectric substrate.
According to another aspect of the present invention there is provided a system for measuring a sound velocity in material, wherein increasing the number of electrode-finger pairs in the first interdigital arrangement makes the directionality of the longitudinal waves sharper under a condition that the total amount of all the finger-areas of the one of the two comb-shaped electrodes in the first interdigital arrangement is constant.
According to another aspect of the present invention there is provided a system for measuring a sound velocity in material comprising a first piezoelectric substrate, a first comb-shaped electrode formed on a lower end surface of the first piezoelectric substrate, a second piezoelectric substrate, a second comb-shaped electrode formed on an upper end surface of the second piezoelectric substrate, a counter electrode cemented between the first- and second piezoelectric substrates, a frequency-sweep oscillator generating input electric signals Ei (i=1, 2, . . . , n) with carrier frequencies fi (i=1, 2, . . . , n), respectively, and a frequency analyzer. A lower end surface of the first comb-shaped electrode is in contact with a surface-part of a material.
When the input electric signals Ei are applied between the first comb-shaped electrode and the counter electrode in turn, longitudinal waves are radiated into the material along the direction vertical to the lower end surface of the first piezoelectric substrate. If the longitudinal waves are reflected at the opposite surface-part of the material, reflected longitudinal waves are detected between the second comb-shaped electrode and the counter electrode as delayed electric signals Di (i=1, 2, . . . , n), respectively. On the other hand, electrical coupled-signals Ci (i=1, 2, . . . , n) from the input electric signals Ei, respectively, are also detected between the second comb-shaped electrode and the counter electrode. The electrical coupled-signals Ci and the delayed electric signals Di, interfere, respectively, so that respective interference signals Ri (i=1, 2, . . . , n) occur. Tracing a dependence of respective amplitudes of the interference signals Ri on the carrier frequencies fi provides a frequency periodicity xcex94f. Thus, a sound velocity V in the material is estimated from the frequency periodicity xcex94f.
According to another aspect of the present invention there is provided a system for measuring a sound velocity in material, wherein the finger direction of the second comb-shaped electrode is orthogonal to that of the first comb-shaped electrode.
According to another aspect of the present invention there is provided a system for measuring a sound velocity in material, wherein the ratio of the interdigital periodicity of the first comb-shaped electrode to the thickness of the first piezoelectric substrate is smaller than four times the ratio of the longitudinal wave velocity in the material to the longitudinal wave velocity in the first piezoelectric substrate.
According to other aspect of the present invention there is provided a system for measuring a sound velocity in material, wherein increasing the number of electrode-finger pairs in the first comb-shaped electrode makes the directionality of the longitudinal waves sharper under a condition that the total amount of all the finger-areas of the first comb-shaped electrode is constant.
According to a further aspect of the present invention. there is provided a system for measuring a sound velocity in material, wherein the input electric signals Ei is accompanied by alternating current bias-signals Si (i=1, 2, . . . , n) with the carrier frequencies fi, respectively. In this case, not the electrical coupled-signals Ci, but the alternating current bias-signals Si, and the delayed electric signals Di interfere, respectively, so that the interference signals Ri occur.